A gas turbine includes a compressor which compresses air, a combustion which combusts a fuel in the air compressed by the compressor, and a turbine which is driven by a combustion gas from the combustor. The turbine includes a turbine rotor which rotates about an axis, a turbine casing which covers the turbine rotor, and a plurality of vane rows which are fixed to an inner peripheral side of the turbine casing. The turbine rotor includes a rotor shaft which extends in an axial direction about the axis and a plurality of blade rows which are fixed to an outer periphery of the rotor shaft and are arranged in the axial direction. The vane row is disposed on an axially upstream side of each blade row. Each vane row includes a plurality of vanes which are arranged in a circumferential direction about the axis. In addition, each blade row includes a plurality of blades which are arranged in the circumferential direction about the axis.
In general, a gap between an inner peripheral surface of the turbine casing and a tip of the blade is referred to as a tip clearance. The turbine efficiency increases as the tip clearance decreases.
For example, as a method of adjusting the tip clearance, there is a method disclosed in the following Patent Document 1. In this method, during a steady state operation of a gas turbine, air is supplied to a plurality of vane rings configuring a portion of the turbine casing and the plurality of vane rings are cooled by the air. In this method, a portion of a compressed air, which is discharged from a discharge port of a compressor and introduced to a combustor, is extracted. In addition, the extracted compressed air is cooled by a cooler, and thereafter, is boosted by a booster. The compressed air from the booster flows into the vane ring of an axially upstream side among the plurality of vane rings, and sequentially flows into the vane ring of an axially downstream side. The compressed air flow out from the vane ring of the axially downstream side is supplied to the combustor to cool the combustor. The compressed air which has cooled the combustor is discharged to the outside of the combustor.